97 KJ?E D Å 7 L7 B7 D9 >; I - SLF

Edited by:
The «Snow Sport Avalanche Accident Prevention» core training team (www.slf.ch/kat), consisting of: WSL Institute
for Snow and Avalanche Research SLF, Davos Swiss Slpine Club (SAC) Federal Office of Sports, Magglingen (BASPO)
Association of Swiss Mountain Guides (ASMG) Swiss Army (Cen exce A mtn tng) Swiss Ski Swiss Snowsports Swiss
Association of Mountaineering Schools (SAMS) Swiss Cableways (SCW) Friends of Nature Switzerland (FNS) Alpine
Rescue Switzerland (ARS) Swiss Council for Accident Prevention (bfu) Suva
With the support of:
MeteoSwiss Swiss Commission for the Prevention of Accidents on Snowsport Runs SKUS Swiss Air Rescue (Rega)
Swiss Foundation for Alpine Research (SFAR) Rescue Organisation of the Canton of Valais (KWRO/OCVS) Swiss
Association of Snowbording Schools (SSBS)
Where to order:
The Editors
Sixth completely revised edition: © 2009
Authors: Stephan Harvey (SLF, Editorial) Jürg Schweizer (SLF) Hansueli Rhyner (SLF) Paul Nigg (Core Training Team
Principal) Bruno Hasler (SAC)
Concept/Graphics: faktorplus und neuweiss communications, Bern
Translation: Levi O‘Neil
Trip with alternatives and schedule
Conditions
Avalanche Situation
(Forecast)
Observations made over the entire day
Conditions
Current avalanche
situation
(Observations)
Collect as much information
as possible regarding
the slope of the key
passage: E.g. Warning
signs, conditions on
similar slopes.
Final risk assessment, trail selection, safety measures, turning
back
Conditions
Avalanche
danger? Visibility?
Do the assumptions
match the reality?
After the tour / descent
Verhältnisse
Terrain
Map / Key
Passages
Decision
Which tour is
feasible?
Verhältnisse
Conditions
Compare different
routes
Decision
Which route?
Terrain
Slope dimensions?
Fall / Burial risk?
Decision
Individual slope
possible?
How?
Go / No Go
Human factors
Patterns
Who?
How many?
Aids
Focus on GRM
GRM
Weigh up pros and cons
Human factors
Beacon Test,
Condition
Aids
Patterns and GRM
are equally important
Patterns
GRM
Weigh up pros and cons
Patterns
Human factors
Aids
Tactics
Focus on Patterns
GRM
Weigh up pros and cons
The avalanche bulletin provides information about snow
conditions and regional avalanche danger for all regions of
the Swiss Alps (local variations are possible). The degree of
avalanche danger depends on: the release probability
(the natural stability of the snow cover and the effects of
human activities), the distribution and frequency of
dangerous slopes, the size and type of avalanches (including
the mass of released snow layers).
National bulletin
(Issue: Daily after 18.30 h)
Distribution:
www.slf.ch
Tel. 187 (from outside Switzerland +41 848 800 187)
MMS: Send an SMS with the text «LAWCHF» to the
number 162
Teletext: Page 782
wap.slf.ch
iPhoneApp «White Risk Mobile»
Weather: www.meteoswiss.ch
Avalanche conditions in adjacent countries:
www.lawinen.org
Characteristics and distribution
New snow
wait
1 – 3 days
The new snow may
release as a slab
Decide
Wind loading
avoid
1 – 2 days
☺
Conditions What is the nature of the avalanche problem (pattern) in the key
passage?
How serious is the risk?
Terrain Where exactly are the dangerous points? What will occur if a slab
releases (size, snow volume, falls, burial)?
Human Factor Can the risk be mitigated to an acceptable level by using the
appropriate strategy (choice of route, cautious behaviour)?
Besides slope angle, aspect, altitude and pattern there are additional factors that are
critical for the decision making process:
Increasing Risk: ☺ Decreasing Risk:
Poor visibility Small group
Large group Small impact on snowpack
Shock loading of snowpack
(jump, fall)
Convex terrain / Undulating terrain
Danger of falling Small slopes and run outs
Slope is below
Defensive route selection
Large slope Frequently skied slope
Regional bulletins
(Issue: Daily after 8 h)
Distribution:
www.slf.ch
MMS: E.g. Send an SMS with the text «LAWZCH» to
the number 162 for the Central Switzerland Avalanche
Bulletin.
Further keywords available with the text
«LAWINE» to the number 162
iPhoneApp «White Risk Mobile»
Western
High Savoy
0033 892 681 020 (*74)
Wet, heavy snow
go early, return early
hours
Northern Slope
of the Alps
Central
Eastern
Bernese Oberland
Vaudois
Fribourg
Alps
Western
Eastern
Northern Alpine Ridge
The Valais
Lower
Main Alpine Ridge
Aosta Valley
0039 0165 776 300
Central Switzerland
Urner
Alps
Gotthard
Region
Eastern
Southern Slope
of the Alps
Piemonte
0039 011 318 55 55
Central
Grison
Bavaria
0049 89 9214 1210
Old snow
ride defensively
days or weeks
Vorarlberg
0043 5522 1588
Tyrol
0043 800 800 503
St. Galler
Apenzeller
Alps
Glarus
Alps
Northern
Grison Lower
The Engadine
Upper
South Tyrol
0039 0471 271 177
Lombardia
0039 0461 230 030
There are weak layers in the snowpack covered with older slabs. Difficult to recognise!
Steep slope above or
terrain trap: danger of deep
burial
Recent drifts may
release as a slab
10 m
Water weakens the
snowpack
Simple risk check combining the factors of danger level,
slope angle and aspect (favorable/unfavorable).
Dangerous expositions are often:
Shady slopes
Wind loaded slopes
Expositions and altitudes specifically mentioned in the
avalanche bulletin.
Avalanche risk in unfavorable aspects:
extremely
steep
40º
very
steep
35º
steep
30º
Moderately
steep
New Snow
Typical signs:
Critical new snow depth
Alarm signs (e.g. recent
slab avalanches)
Typical distribution:
Dangerous areas cover a
wide area
Danger often increases
with altitude
Tips:
Few avoidance
possibilities
GRM useful
General Precautions:
Keep track of the weather and avalanche situation,
plan adequately
Keep others informed of your intentions and route
choices
Always have your beacon set to TRANSMIT (function
tests), always carry shovels and probes
Constant reassessment of: weather, snow, terrain,
schedule and human factors
Conditions:
Critically assess recent snow drifting
Consider the variations in temperature depending on
the time of the day and the impact of radiation
In foggy or low visibility conditions be prepared to
turn back if you find yourself in steep, unknown terrain
or critical conditions!
Terrain:
Terrain over 30° is potential
avalanche terrain.
Low,
track
Moderate,
area of the track
(20m)
Considerable,
entire slope *
Steepest section: ca. 20 m x 20 m
Wind Loading
Typical signs:
Signs of snow drifting
May be hard packed or
soft
Irregular when breaking
trail
Cohesive snow
Alarm signs (e.g. recent
slab avalanches,
cracking)
Typical distribution:
Wind shadows (leeside,
terrain breaks, gullies)
Often found at high altitude
and ridge areas
Variation within a small
area
Tips:
Avoid when possible
Recent snow drifts are
often dangerous over
30° of slope angle
GRM not always applicable
Descend extremely steep slopes and key passages
one at a time
Avoid the steepest sections of any given slope
Avoid steep, rocky outcrops and gullies
high, entire
slope including
deposition zone
If we do not know the conditions, if we can’t make observations,
or if the unfavourable slopes are not specified in
the bulletin, we assume all slope aspects to be unfavourable.
If there is a difference, we may assume a lower
danger for the slopes of favourable aspects (typically
about one degree lower).
High risk
Snowsport not recommended!
Elevated risk. Caution! Experience necessary!
Patterns, weigh up pros, cons with the focus on the
avalanche risk on the individual slope.
Intelligent route choice and intelligent behaviour
Inexperienced riders should avoid this area
Training and experience necessary
Low risk
Relatively safe if no particular danger signs are present
Inexperienced skiers and boarders should stay below
this line.
* If at considerable danger remote triggering or large avalanches are
unlikely (often the case with constantly travelled off-piste runs/popular
tours), then it may be possible that not the entire slope must be considered.
Wet Snow
Typical signs:
Rain
Overcast (reradiate
outgoing radiation)
High temperature /
strong solar radiation
Deep penetration
Natural avalanche
release (slab, loose
snow)
Typical distribution:
Varying aspects and
altitudes (dependent on
time of year / day)
Often found near warm
rocks
Tips:
Return early
Wait for cooling
Beware of large naturally
triggered avalanches
GRM not always applicable
Human Factors, Behaviour
Old Snow
Typical signs:
Weak layer within the
snowpack
Alarm signs (whumpf
sounds)
Typical distribution:
Regions / zones with
relatively shallow snow
cover
Terrain transitions (e.g.
from flat to steep or
from ridge to bowl)
Rocky outcrops
Often found on north
facing slopes
Tips:
Simple snowpack tests
often useful
Difficult to recognise
Pay attention to bulletin
information
GRM may be useful
Maintain distance between riders/skiers (ascent
5 – 10 m, more by descent) or descend one at a time
• Define a descent corridor, ride (ski) carefully, avoid
falls
• Stop and regroup on «islands of safety»

GEFAHRENSTUFE CHARACTERISTICS (RELEASE PROBABILITY, DISTRIBUTION AND FREQUENCY OF
DANGEROUS SLOPES, TYPE OF AVALANCHES)
1
LOW
GERING, FAIBLE, DEBOLE
2
MODERATE
MÄSSIG, LIMITÉ,
MODERATO
3
CONSIDERABLE
ERHEBLICH, MARQUÉ,
MARCATO
4
HIGH
GROSS, FORT, FORTE
5
VERY HIGH
SEHR GROSS
TRÈS FORT, MOLTO FORTE
Slope Angle Classifications: moderately steep terrain: slopes flatter than about 30° very steep slopes: slopes steeper than 35°
steep slopes: slopes with an angle of more than about 30° extreme slopes: steeper than 40° and slopes that are inherently dangerous due to terrain profile or close proximity to ridges.
NEW SNOW
Critical new snow depth =
at least considerable avalanche danger
10-20 cm when conditions are unfavourable
20-30 cm when conditions are fair or mixed
30-50 cm when conditions are favourable
Favourable:
low to moderate winds, air temperature close to 0°C,
highly irregular old snow surface, frequently skied slope
Unfavourable:
high rate of precipitation (heavy falls within a short time),
strong winds (>40 km/h, roaring wind), low temperature
(below -5 to -10°C), smooth or loose old snow surface,
rarely skied slope
Alarm signs
(typical for danger levels of considerable and
above)
Recent, natural and remotely triggered slab avalanches.
Whumpf sounds and cracking.
Steepness
Measure the slope angle with an inclination scale on the
map (1:25‘000). Attention: S-shaped terrain profiles are
always steeper in reality
Steepness measured
Steepest part
Slope with S-shaped
During the trip, estimate or measure the inclination of the
steepest part of the slope (ca. 20 m x 20 m).
Also consider steep slopes above and below the route, in
particular from considerable danger on upwards.
Shape of slope and type of terrain
Most accidents occur on steep, shady slopes near ridge
tops
Hilly ground allows for better selection of a safe route.
Sparse woods do not protect from avalanches.
Ridges are generally safer than gullies.
Steepness averaged over 100m vertical
(Homogenised Slope Angle!)
Triggering is generally possible only with high additional loads (e.g. groups without intervals) and on very few
locations in steep extreme terrain. Only a few sluffs and small natural avalanches are possible. Forecasted for
about 20% of the winter season. About 7% of the recreational fatalities.
Triggering possible in particular with high additional loads, particularly on the steep slopes indicated in the
bulletin. Large natural avalanches not likely.
Forecasted for nearly 50% of the winter season. About 34% of the recreational fatalities.
Triggering possible even with low additional loads (e.g. single person), particularly on the steep slopes indicated
in the bulletin. In some conditions, medium and occasionally large natural avalanches may occur.
Frequently alarm signals exist (whumpfs, natural releases).
Forecasted for nearly 33% of the winter season. About 47% of the recreational fatalities.
Triggering probable even with low additional loads on many steep slopes of all aspect. In some conditions,
many medium and several large natural avalanches are likely.
Forecasted for a few days only of the winter season. About 12% of the recreational fatalities.
Numerous large natural avalanches are likely, even in moderately steep terrain. Avalanches run to the valley
bottom.
Rarely forecasted, on average for one day of the winter season. No recreational fatalities.
20m
20m
Avalanche danger prevails with:
- Wind and new snow.
- Rapid and intense warming.
- Weak layers in the snowpack.
Aspect
Shaded (cold) slopes are often less stable than sunny
slopes.
Sunny slopes may become critically unstable under
conditions of intense warming.
Slope Dimensions, Slope Run Out.
How much area does the slope cover, does the lower
section run out?
Is there a danger of being swept over terrain forms or
being buried in hollows or riverbeds?
Is there an increased danger of injury through collision
with boulders or trees?
Measuring Methods: with help from ski poles of equal
length or with angle indicators.
Rules of Thumb: Kick turns required during ascent > ca.
30º; Piles of rubble under cliff walls ~ 35°; Steep, rocky
terrain or glacial moraine > ca. 40º.
If the suspended pole contacts the snow surface
below the mark the slope is steeper than 30°, 10cm
of difference to the initial mark represents some 3°
of slope angle.
Class of steepness
10cm
30º 36º39º
30º
WIND
CONSEQUENCES AND RECOMMENDATIONS FOR RECREATIONISTS OUTSIDE OF
CONTROLLED SKI AREAS
Generally favourable conditions.
Ski one by one on extremely steep slopes. If possible avoid recent accumulations of wind-driven
snow on extreme slopes. Beware of the danger of falling and of possibly unfavourable conditions
in high alpine terrain.
Favourable conditions, for the most part. Routes should be selected with care, in particular
on steep slopes of the aspect and altitude indicated in the bulletin. Avoid all extremely
steep slopes of the aspect and altitude indicated in the bulletin and recent accumulations of
wind-driven snow. Ski one by one and with caution on very steep slopes.
Partly unfavourable conditions. Critical situation. Experience in avalanche hazard
assessment and in selecting good routes required. Avoid very steep slopes of the aspect and
altitude indicated in the bulletin if possible. Pay attention to remotely triggered avalanches.
Proceed with caution on traverses or when travelling into unknown terrain.
Unfavourable conditions. Acute Situation. Lines of transport might be endangered.
Sound experience in avalanche hazard assessment required. Stay in moderately steep terrain;
beware of runout zones. Remotely triggered avalanches are typical, even over large distances.
Very unfavourable conditions. Catastrophic situation. Parts of villages endangered,
evacuations might be necessary.
Travel in avalanche terrain not recommended.
Wind is the architect of slab avalanches through the creation
of wind slabs. Conditions for wind slab formation:
Sufficiently strong wind
Erodible snow surface or new snow
Wind slabs may be hard packed or soft, often displaying
highly uneven distribution in lee areas.
Human factors often play a deciding role in avalanche
accidents. Recognition of dangers, the decision making
process and behaviour may be influenced by perception
failures and lack of communication.
Illusions/Limits of perception:
Slope steepness is underestimated when looking
from above or on sunny slopes.
Hard packed snow feels safer than soft snow.
It is difficult to estimate terrain forms in low visibility.
Storm winds mask whumpf sounds.
Travelling in a group offers a false sense of security.
Tracked out slopes appear to be safe.
Communication:
Have the goals and expectations been discussed?
Have group members clearly understood directions
from the group leader and will they be followed?
Can I rely on my touring partners?
Recent wind slabs are easily triggered.
Perception traps:
Commitment / Wishful Thinking:
We often only see what we expect and want to see.
We tend to filter information in favour of our plan.
Familiarity/Positive reinforcement:
Familiar terrain feels safe. («there has never been a
slide here.» «It has been fine until now.»)
Scarcity:
We experience an urge to ride or ski an unridden
slope. The euphoria of exclusivity often hinders our
ability to think clearly.
Group:
Tendency of groups to take higher risks: risky shift
effect, group/peer pressure, competition within and
between groups. Presence of other groups or ski
tracks.
Always take a bad feeling seriously. Continuously weigh up your good feelings against new
observations and facts: do not be led astray.
TYPES OF AVALANCHES (DRY OR WET)
WATER
Snow slab avalanche
Wet Snow Situation
Water weakens the snowpack and may cause wet snow
avalanches. They generally release naturally and are
seldom triggered by skiers or boarders.
Typical Wet Snow Avalanche Situation:
Rain or melt water flowing into a dry snowpack
leading to marked weakening at layer boundaries.
(rain in midwinter, first heavy melt phase of the snowpack
due to solar radiation in March).
Loss of strength through uniform wetting of the
snowpack. Collapse of weakened base layers (spring).
If the snow surface is distinctly refrozen, following a
clear night, mostly favourable conditions prevail before
midday. Pay attention after midday and generally at any
time when the sky is overcast. Pay attention to
diurnal variation!
Loose snow avalanche
About 90% of all avalanche victims have triggered the fatal avalanche themselves.
TEMPERATURE
Take into account previous and expected variations. Cold
temperatures prolong the danger. Warm temperatures
have a long term stabilizing effect. Particularly repeated
warming and cooling cycles.
Rapid, distinct warming towards 0°C increases instability.
Solar radiation significantly warms the surface layers,
thereby promoting instability.
SNOW SLAB AVALANCHES
Cohesive snow on top of a weak layer: The slab breaks away
as a unit. Dry snow slabs are the most dangerous avalanches
for snow sport. They are also possible when the surface layers
seem to consist of cohesionless powder snow.
Typical dry snow slab avalanche situations:
Unstable new snow (new snow situation)
Unstable wind slab (wind loading situation)
Old snow on top of a weak layer (old snow situation)
Terrain
Critical steepness: (steepest slope section, ca. 20 m x 20 m in
crown area): 30°. The majority of slab avalanches release at
a slope angle between 35° and 45°. A slab may also be
released from adjacent flat terrain (remote triggering)
Beware of runout zones!
Avalanche release (spontaneously or artificially) by
either an increase in stress (e.g. by a skier) and/or a
decrease in strength (e.g. by warming or rain).
SNOWPACK LAYERING
Often favourable under the following conditions:
Deep snowpack
Similar layers
Critical layers (often soft layers) more than 1 meter below
the snow surface
Often unfavourable under the following conditions:
Shallow snowpack
Large differences between layers, e.g. hardness and grain size.
Critical layers (often soft layers) in the upper meter of the
snowpack.
Assessing the snowpack becomes more important when
there are no obvious alarm signs, wind loading or critical
new snow depth pointing to avalanche danger.
Snowpack observations
• Penetration Depth (with or without skis): Allows the
identification of weaker base layers in a relatively thin
snowpack. Thinner layers are not easily recognised by this
method. • Pole Test: Allows the identification of differing
hardness between layers. • Snowpack Tests (e.g. column or
block tests): Allows the identification of weak layers and an
estimation of their strength. • SLF Snowpack Stability
Maps: Provide a general tendency of the snowpack characteristics
in a given region.
IF CAUGHT
Try to escape out of the avalanche area, let go of your ski
poles, try to open bindings (rarely possible), pull your
knees toward your chest and hold your arms in front of
your face. Fight like hell!
IF NOT CAUGHT
Vanishing Point
entry tracks
about 40 m*
Watch the avalanche flow and the persons caught
(note the last seen point)
Gain an overview – think – act. Assess your own
safety, avoid further accidents
Determine primary search area (in the direction of
flow below the last seen point)
Q
Q
Q
Q
Q
Q
Q
Temperature 0 C
0
-10
24h 24h Time
Begin searching immediately with eyes, ears and
transceiver (turn off transceivers that are not in use)
Pinpoint search with avalanche probe
Alert rescue service. (Telephone, Radio, Runner (when
possible in pairs)
(* Search strip widths: Minimum 40 m with analog devices. Follow
manufacturer recommendations for digital devices.)
If transceivers are not available:
Search with eyes and ears
Alert rescue service
Systematic repeated improvised probing
BURIAL BY AVALANCHE = DANGER OF DEATH!
Chances of Survival
Only 50% of completely buried
victims are recovered alive.
Burial Time (min)
Methodical, V-shaped digging
Uncover head and chest as fast as possible, clear the
breathing passages, check if there is a breathing cavity in
the snow (Snow filled airway = No breathing cavity)
Start artificial respiration (mouth-to-nose), if circulation
has stopped, start cardiopulmonary resuscitation simultaneously;
continue resuscitation until a medical doctor
takes over
Prevent further cooling
Position the victim according to injury
Watch and take care of the victim very carefully
Careful evacuation by helicopter
ALARM
Phone: Swiss air rescue (Rega): 1414 (all of Switzerland,
except in Valais); International Emergency: 112, KWRO/OCVS:
144 (Valais)
Radio: 161.300 MHz (E-channel)
158.625 MHz (K-channel, police)
ACCIDENT REPORT
Who is calling (Name, phone number, location)?
What happened?
Where is the accident location?
When did the accident happen?
How many completely buried victims, helpers?
Weather in the area?
Transceiver, Recco?
LOOSE SNOW AVALANCHE
Loose snow avalanches often release in terrain steeper than
40°. They travel slowly in comparison to slab avalanches.
Loose snow avalanches are often formed from cohesionless
new snow or wet snow.
The first sunny day after a snowfall tends to be
especially dangerous.
Snowpack Tests
Distinct fracture following easy loading indicate critical layering.
Weak layers are often soft and coarse grained.
AIR RESCUE
Do not approach the helicopter before the rotor has stopped.
Only embark or disembark in the company of a crew
member when the rotor is turning. Always stay in contact
with the pilot.
Landing Place Hazards
Ensure no loose objects are left lying in the area
Pay attention to skis, avalanche probes, etc.
Concise report = Effective help